KVM: arm64: nv: Don't adjust PSTATE.M when L2 is nesting

KVM: arm64: nv: Don't adjust PSTATE.M when L2 is nesting

We currently check for HCR_EL2.NV being set to decide whether we
need to repaint PSTATE.M to say EL2 instead of EL1 on exit.

However, this isn't correct when L2 is itself a hypervisor, and
that L1 as set its own HCR_EL2.NV. That's because we "flatten"
the state and inherit parts of the guest's own setup. In that case,
we shouldn't adjust PSTATE.M, as this is really EL1 for both us
and the guest.

Instead of trying to try and work out how we ended-up with HCR_EL2.NV
being set by introspecting both the host and guest states, use
a per-CPU flag to remember the context (HYP or not), and use that
information to decide whether PSTATE needs tweaking.

Reviewed-by: Oliver Upton <oliver.upton@linux.dev>
Link: https://lore.kernel.org/r/20250514103501.2225951-7-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>